Implantable medical devices based on microchips that include reservoir arrays containing biosensors or drugs, for example, are known in the art. FIG. 1 shows a possible conventional approach for assembly of components in an implantable medical device 10, which includes a microchip assembly 12. The microchip assembly 12, which is also referred to as a microchip element, includes microreservoirs, each of which may contain a drug for controlled delivery in vivo or a sensor for controlled exposure in vivo. The microchip assembly 12 is attached to a feedthrough 16 that is welded to the housing 14. Such microchip assemblies or elements are described, for example, in U.S. Pat. No. 7,510,551 to Uhland et al. and U.S. Pat. No. 7,604,628 to Santini Jr. et al. The feedthrough 16 contains electrically conductive pins that are metallurgically brazed to metallized surfaces on and through an alumina disc. A typical pin count exceeds 100, and in more complex designs, can be over 400. The consequence of such designs is that each pin connection can be a leak point.
In addition, each feedthrough pin is electrically connected to an electronic component inside the housing. Some designs utilize a wire from the pin to the circuit, while the illustrated design attaches the feedthrough 16 directly to a conventional plastic circuit board 18. These electrical connections require testing to ensure continuity. As a result, the pin count impacts the cost of the feedthrough, and that cost increases as the number of feedthrough pins increases in the implantable device. Consequently, due to this complex design requirement, the resulting manufacturing, and the required acceptance tests, the feedthrough is an expensive component.
Moreover, conventional implantable device designs based on a feedthrough or header attached to housing components disadvantageously have an overall volume of the resulting device that is larger than desired, because several discrete components make up the assembly.
The devices shown in FIG. 1 contains control electronics, a power source, and wireless communication capabilities. The benefit of these internal functions is that the device can be programmed to automatically release discrete doses at specific time points, and the dosing schedule can be updated or modified wirelessly at any time. The patient therefore can automatically receive his or her medication without having to take any action. A disadvantage to this automatic drug delivery implant is that all of these functions require a finite volume. There is a clear desire, however, to reduce the volume of the device in order to i) reduce the incision required to implant the device under the skin, ii) increase the possible locations in the body that the device can be implanted, and iii) make the device less intrusive for the patient. In particular, it would be desirable to provide a smaller overall device volume without sacrificing functionality, simplicity, and/or hermeticity.